The Q/U Imaging ExperimenT (QUIET) was a Cosmic Microwave Background (CMB) polarization experiment operating in the Atacama Desert, Chile. QUIET had two receivers - the 40 GHz (Q-band) receiver was deployed to the observation site in August 2008, and wrapped up data taking in June 2009. The 90 GHz (W-band) receiver finished taking data in December 2010. Columbia was responsible for building both receiver cryostats, internal electronics, for integrating, testing, and deploying the Q-band receiver, and for much of the observing and data analysis for the Q-band receiver.
The cryostat design required an extensive research and development effort for the vacuum windows. Each window was roughly 22" in diameter, the largest for a CMB experiment at the time. We tested window materials and thicknesses, as well as methods for coating the windows with an appropriate antireflection material. Both cryostats have successfully operated in the field maintaining the QUIET polarization modules near 20 Kelvin cryogenic temperatures, our requirement for optimal performance.
The QUIET polarimeters (hereafter: modules) were developed by our collaborators at the Jet Propulsion Lab (JPL). They leveraged work done for the CMB satellite Planck for the design of individual module components (radio frequency amplifiers, phase switches, and hybrid couplers), and created an innovative integrated chip design incorporating these components. This miniaturized the entire receiver chain from ~12"x6" to the 1"x1" QUIET modules, which enabled QUIET to construct a large-format array of coherent polarization sensitive modules for the first time. The QUIET modules are unique among CMB experiments in that they coherently measure the polarization stokes Q and U vectors simultaneously on 100 Hz time scales. At Columbia we tested prior to deployment: polarized array sensitivity, module noise performance, module bandpasses, and thermal control and stability for both cryogenic and bias-board temperatures. The array performance met sensitivity benchmarks and have operated at expected sensitivity levels during the season.
We spent six weeks integrating the telescope and receiver at the Caltech Institute of Technology, and performed final receiver checks before shipping the experiment to Chile for deployment. The Columbia group made up the first deployment team, travelling to Chile to integrate the receiver and telescope on the CBI mount. The Q-band array logged over 3500 hours of on-sky time before removing the Q-band receiver, after which the W-band receiver was deployed.
Columbia is collaborating with the University of Oslo and Oxford University to develop and use a maximum likelihood pipeline for analyzing the season of Q-band data. We are currently developing and testing data cutting strategies.